1. Field of the Invention
The present invention relates generally to telecommunications networks and, more particularly, to employing sealing currents in such networks.
2. Background of the Invention
DSL (Digital Subscriber Line) technology provides high-speed data services over ordinary copper telephone lines. ADSL (Asymmetrical Digital Subscriber Line) is a type of DSL common for residential use. ADSL can download data much faster than it can upload data. SDSL (Symmetric Digital Subscriber Line) is a type of DSL service commonly made available to business users. Unlike ADSL, SDSL offers equal upload and download speeds. Types of SDSL service include SHDSL (Symmetric High Bit-rate Digital Subscriber Line) and EDSL (Enterprise Digital Subscriber Line), both of which are increasingly being offered to corporate users.
FIG. 1 illustrates a typical communication network architecture that provides SDSL services and POTS (Plain Old Telephone Service). FIG. 1 includes telephone user 108 and computer system 118. Computer system 118 may be any type of computer system capable of receiving and transferring data such as a personal computer or a main frame computer.
Telephone user 108 connects to OE (Office Equipment) 104 through connector module 106, via twisted-pair POTS line 110. Connector module 106 may be a lightning surge protector module. Connector module 106 may be located in a Central Office building 101 or a Remote Terminal enclosure 111. OE 104 connects telephone users 108 to the PSTN (Public Switched Telephone Network) 102 thereby providing well-known POTS functionality to customers.
Computer system 118a connects to DSLAM (DSL Access Multiplexer) 114 through connector module 116, via twisted-pair DSL service line 120. Connector module 116 may also be a lightning surge protector module. Connector module 116 and DSLAM 114 may be located in a central office building 101 or a Remote Terminal enclosure 111. DSLAM 114 connects computer system 118 to Network 112, such as the Internet, thereby providing DSL services to customers in a known fashion.
As is well-known in the art, OE 104 and DLC 126 both provide a sealing current that causes a small amount of DC current to flow through POTS lines 110. OE 104 may be a Line Port at the central office of PSTN 102 or a Line Port on the PSTN that is extended to a Remote Terminal enclosure 111 over a DLC system 126. Sealing current prevents corrosion build-up, reduces poor connections and noisy lines and improves overall transmission characteristics. Sealing current is a major contributor to telephone network reliability in the POTS arena.
In the DSL arena, however, and more particularly, in connection with SHDSL and EDSL services, the DSLAM that provides the SHDSL and EDSL services does not always have the capability of generating sealing current. Accordingly, when these DSL services are provided, a separate sealing current unit must be installed to provide and connect sealing current to the DSL twisted copper pair. When the DSLAM 114 is located in a Remote Terminal Enclosure 111, the addition of the sealing current unit must be co-located inside the corresponding remote enclosure, requiring mounting space and power, as commercially-available sealing current units are typically provided in the form of separate rack-mounted units. To complicate matters, particularly in the context of a large telecommunications service provider, an OSPE (Outside Plant Engineering) EWO (Engineering Work Order) is typically required to purchase physical plant devices such as sealing current units. Since sealing current units must be deployed before service is first made available from a RT (Remote Terminal) site, service to the customer may be unnecessarily delayed until after the EWO can be processed and the sealing current unit is purchased and installed.
Further, it is difficult to determine whether a given customer facility might require sealing current service. Thus, to ensure quality service and customer satisfaction, sealing current units are often preinstalled at all remote sites, thereby increasing cost, perhaps unnecessarily, to the telecommunications service provider.